Salons. Un éclairage sur la société par les revues savantes.

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Recent research published independently by scientists in Canada and the U.S. indicates there is cause for great concern over the growing prevalence of herbicide-resistant weed biotypes within the Amaranthaceae family. Various species of herbicide-resistant weeds have been problematic for years, but the reproductive capacity, long-range dispersal capability, and potential for gene flow among Amaranthus spp. warrants special concern for crop producers. In gene amplication-polymerase chain reaction experiments, McNaughton et al. (2005) showed that A. powellii (Powell amaranth) and A. retroflexus (redroot pigweed) populations sampled from various locations in Ontario were resistant to acetolactate synthase (ALS)-inhibiting herbicides by virtue of one of four different resistance-conferring ALS gene mutations found among the populations tested. The different resistance mutations were associated with geographically different populations, suggesting that herbicide resistance evolved simultaneously at different locations. In related news, Patzoldt et al. (2005) confirmed the presence in Illinois, USA of an A. tuberculatus (waterhemp) biotype with multiple resistance to herbicides representing three unique sites of action: ALS inhibitors, protopor-phyrinogen oxidase (PPO) inhibitors, and Photosystem II inhibitors. The collective findings of these papers suggest that herbicide options for controlling Amaranthus spp. are of dwindling utility because resistance can develop quickly and across sites of action in response to strong herbicide selection pressure.